in vitro bioactivity of a tricalcium silicate cement
TRANSCRIPT
IN VITRO BIOACTIVITY OF A TRICALCIUM SILICATE CEMENT
Morejon-Alonso L.(1), Bareiro O. (1), Dos Santos L.A.(1), Garcia Carrodeguas R.(2)
(1) Escola de Engenharia, Dep. de Materiais, Universidade Federal do Rio Grande do Sul, Porto Alegre (RS), Brasil, [email protected]
(2) Departamento de Cerámica, Instituto de Cerámica y Vidrio - CSIC, Madrid, Spain
ABSTRACT
Tricalcium silicate is the major constituent of Portland cement and the responsible for their mechanical strength at early stages. In order to be used as and additive of conventional calcium phosphate cement (CPC), in vitro bioactivity of a calcium silicate cement (CSC) after soaking in simulated body fluid (SBF) for 14 days was study. The cement was obtained by mixing Ca3SiO5, obtained by sol-gel process, and a Na2HPO4 solution. The morphological and structural changes of the material before and after soaking were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed the formation of a layer of a Hydroxyapatite (HA) onto the CSC cement after soaking for 1h in SBF that became denser with the increase of soaking time. The study suggests that Ca3SiO5 would be an effective additive to improve the bioactivity and long term strength of conventional CPC.
Keywords: Tricalcium silicate, calcium silicate cement, calcium phosphate cement, in vitro.
INTRODUCTION
Ca3SiO5, also named C3S, is considered the most important constituent of
ordinary Portland cement (OCP) due to their spontaneous development of strength
(spontaneous consolidation) towards water and their influence on the setting time of
pastes (1).
Although it is quite known that silicon-containing materials have bioactive
properties (2,3) and recent studies showed that C3S powders (4), cement based (5) and
ceramics, could induce the formation of hydroxiapatite (HA) after soaking in SBF and
had a stimulatory effect on cell growth in a certain concentration range (6); it is
unknown the effect of some additives to a liquid component for the use of C3S as a
self-setting material or as an additive for others hydraulic cements.
On the other hand, calcium phosphate cements (CPC) are widely used as bone
repairing and substituting materials in many dental and orthopedic applications due
to their excellent biocompatibility, osteoconductivity and osteotransductivity (7).
Particularly, α-TCP-based CPC, when mixed with aqueous Na2HPO4 solution, set as
the result of the dissolution of α-TCP particles and the precipitation of an
entanglement of calcium deficient hydroxiapatite (CDHA) crystals (8). For these
materials, the low mechanical strength is their main limitation, and controlled addition
of C3S could be an effective way to increase the strength of them. Thus, the aim of
this work was to study the in vitro bioactivity of a Ca3SiO5/Na2HPO4 cement, in order
to use C3S as and reinforcement additive for conventional α-TCP-based CPC.
MATERIALS AND METHODS
Tricalcium silicate powders were synthesized by sol–gel route (4), using
Ca(NO3)2.4H2O and Si(OC2H5)4 (TEOS) as precursors and calcined at 1400°C for
48h. Cements were obtained by mixing C3S powders (mean diameter of particle size
14,56 µm) and 2.5 wt./vol. % Na2HPO4 aqueous solution in a liquid/solid ratio of 0.4
mL/g. Pure distilled-deionized water was also used as mixing liquid to prepare control
samples.
In vitro bioactivity study was carry out in simulated body fluid (SBF) prepared
according to the procedure described by Kokubo (9) at 36.5°C using a ratio
volume/area of 0.1 cm3/mm2. The 24h-set pastes were soaking in SBF for 14 days,
and after preselected soaking time, gently rinsed with deionized water followed by
drying at room temperature.
Mineralogical composition of C3S was determined by X-Ray Diffraction (XRD) in
a PHILLIPS diffractometer (X´Pert MPD) and Cu-target. Diffractograms were
recorded employing Ni-filtered radiation (λ = 1.5406 Å), and anodic voltage and
current of 40 kV and 40 mA, respectively. The step size was 0.05° and the time/step
ratio was 1 second.
Morphological variations before and after soaking in SBF were characterized by
Scanning Electron Microscopy (SEM) using a JEOL microscope (JSM-6060).
Samples were previously coated with a thin layer of gold.
RESULTS AND DISCUSION
Fig. 1 shows the XRD pattern of the C3S powder. The results showed that
Ca3SiO5 was formed as principal phase (JCPDS 13-0209, 09-0352), however the
most intense characteristic peaks for CaO (JCPDS 37-1497) were founded; probably
owing to the evaporation of TEOS during the synthesis, even though the reaction
took place under stoichiometric conditions (Eq. A). This result is in contradiction with
previous studies reported, in which C3S can be obtained without free CaO, at
temperatures above 1400°C with calcinations times of 2h (4).
3�������. 4�� ��� � ��������� � ������� ��� � 4����� � 6�� � 10�� ��� �
3 2 � ���⁄ (A)
Figure 1. X Ra X-Ray diffraction patterns of Ca3SiO5 powder. � Ca3SiO5, � CaO.
Figure 2 shows the SEM micrographs of the surface and cross-section of the
pastes after 1 day-set. In the surface of cement it was found the characteristics
aggregated of needle-like crystals of calcium silicate hydrate gel (C-S-H) type I (Fig.
2A) and platy-type II C-S-H (Fig. 2B) (10). Higher magnifications of surface showed
typical hexagonal habits of Ca(OH)2 who growth into a void, where space restrictions
are minimal, allowing development of euhedral forms. In cross-section, the pore size
10 20 30 40 50 60 70
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nsity
(co
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/s)
2 θ (Degrees)
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was larger than those on the surface, and tiny particles aggregated, probably of C-S-
H gel were observed (Fig. 2D).
Figure 2. SEM micrographs of the surface and fracture surface. (A), (B) and (C)
surface; (D) cross section.
Fig. 3 shows the SEM micrographs of cement after soaking in SBF at different
times. Before soaking, the paste showed compact structure with some micropores.
After soaking for 1h, tiny ball-like particles were observed on the surface of the
samples (Fig. 3A and B). After soaking for 1day, the layer of HA became denser (Fig.
3C) and higher magnification SEM micrograph showed that the particles of HA were
worm-like and many of these particles formed agglomerates (Fig. 4D and F). Seven
days after, micropores disappeared, and a compact HA layer of just about 250µm is
formed on the surface (Fig. 3E).
(A) (B)
Ca(OH)2
CSH
CSH
CSH
(C) (D)
Figure 3. SEM micrographs of the surfaces of Ca3SiO5 paste after soaking in SBF
solution for 1h (A, B), 1 day (C, D) and 7 days (E, F).
(A) (B)
(C) (D)
(E) (F)
CONCLUSIONS
C3S can be syntethized by sol-gel method, although considerable free lime is
present in final product, which can causes an increase in local pH. The formulation
Ca3SiO5/ Na2HPO4 could induce the formation of HA after 1h soaking in SBF and the
layer after one week has 250µm of thickness. For that reason C3S would be an
effective additive to improve the bioactivity and long term strength of conventional
CPC.
ACKNOWLEGMENTS
This work was conducted with support from CAPES, the Brazilian Government
entity dedicated to the training of human resources.
REFERENCES
1. Lea F. M. The Chemistry of Cement and concrete. London: Edwuard Arnold
Ltd., 1970.
2. Kokubo T., Bioactivity of bioglasses and glass ceramics. In: Bone-bonding
biomaterials. Leidendorp: Reed Healthcare Communications, 1992, p.31-46.
3. Hench L., W.J., Biological applications of bioactive glasses. Life Chem. Rep.,
v.13, p.187-241, 1996.
4. Zhao W., C.J., Sol–gel synthesis and in vitro bioactivity of tricalcium silicate
powders. Materials Letters, v.58, p.2350- 2353, 2004.
5. Zhao W., W.J., Zhai W., Wang Z., Chang J., The self-setting properties and in vitro
bioactivity of tricalcium silicate. Biomaterials, v.26, p.6113-612, 2005.
6. Zhao W., C.J., Wang J., Zhai W., Wang Z., In vitro bioactivity of novel tricalcium
silicate ceramics. J. Mater. Sci.: Mater. Med., v.18, p.917-923, 2007.
7. Lee B. H., K.M.C., Kim K. N., Kim K. M., Choi S. H., Kim C. K., Legeros R. Z., Lee
Y. K., Preliminary Investigation of bone cement using Calcium phosphate glass. Key
Eng. Mater., v. 284-286, p.109-112, 2005.
8. Driessens F. C. M., K.C., Planell J. A., Gildenhaar R., Berger G., Reif D., Fitzner
R., Radlanski R. J., Gross U., Evaluation of calcium phosphates and experimental
calcium phosphate bone cements using osteogenic cultures. J. Biom. Mater. Res.,
v.52, p.498–508, 2000.
9. Kim H. M., M.T., Kokubo T., Nakamura T., Revised Simulated Body Fluid. Key
Eng. Mat., v.192-195, p.47-50, 2001.
10. Stutzman P., Scanning Electron Microscopy in Concrete Petrography. In
Materials Science of Concrete: Calcium Hydroxide in Concrete. Florida: The
American Ceramic Society, 2001, p.59-72.